We will record the electrical response of single cells in the cat visual system to simple and complex patterns of illumination. We will measure the magnitude and time course of these responses. We will study the activity of retinal ganglion cells, cells in the lateral geniculate nucleus, and cells in the striate and non-striate visual cortex of the cat. A related study will be undertaken on the response of vertebrate retinal cells to complex patterns of illumination. We will be able to control stimulus contrast, temporal frequency, spatial frequency of gratings, orientation, direction, and velocity of motion. Precise measurement of the spatial sensitivity distributions, the spatial frequency response and the dynamics of responses will enable us to determine whether visual neurons may be classified properly as feature detectors or as broadly tuned, linear spatial-temporal filters.